It should be super easy using dd...
sudo dd if=/dev/mydrive of=image.iso
You could also clone one drive to another like this:
sudo dd if=/dev/mydrive of=/dev/myothersd
Just be careful. "if" is the input file and "of" the output file. Messing up these values could nuke your system. Make sure you know what drive is what using:
sudo fdisk -l
when you figure out what drive you want to use your command will look something like this (to clone the entire drive):
sudo dd if=/dev/sda of=mydrive.iso
DO NOT just copy and paste the above command or any dd command. When using dd ALWAYS confirm correct drive paths!
An example of cloning a partition, looks like this:
sudo dd if=/dev/sda1 of=mydrive.iso
For more information, check out the manpage
Note: When using dd, it gives you no progress or output while it's doing its thang. It will take a while and show no progress, don't worry, just wait.